First genetic code of Neanderthal reveals interbreeding

06 May 2010

Neanderthal scene. Scientists have produced the first whole genome of Neanderthals revealing clues about their interbreeding with modern humans.

The genetic code of the Neanderthals has been revealed for the first time, giving surprising clues to their intimate relations with modern humans, scientists report in the journal Science today.

Neanderthals are usually regarded as a separate species, Homo neanderthalensis. They were our closest relatives and they died out about 30,000 years ago.

An international team, including those at the Max Planck Institute in Germany, analysed DNA from the remains of 3 Neanderthal individuals. They produced a sequence of the whole Neanderthal genetic code, or genome, the first time this has been done.

They also compared the Neanderthal genome to modern humans, Homo sapiens, from different parts of the world.

Evidence for interbreeding

Until now, scientists could only speculate whether Neanderthals ever interbred with modern humans, but the team’s results revealed some surprises.

Model head of a Neanderthal man

They show that modern humans outside of Africa share genetic information with Neanderthals. This means modern humans probably interbred with Neanderthals soon after they left Africa around 60,000 years ago.

Professor Chris Stringer, the Natural History Museum’s human origins expert, comments on the research and explains, 'This research suggests that the genomes of people from Europe, China and New Guinea lie slightly closer to the Neanderthal sequence than do those of Africans.

'The most likely explanation for this finding is that the ancestors of people in Europe, China and New Guinea interbred with Neanderthals (or at least with populations that had a component of Neanderthal genes) in North Africa, Arabia or the Middle East, as they were exiting Africa, but before they spread out across the rest of the world.’

Prof Stringer is one of the architects of the Out of Africa theory, which explains how all humans living today share an African origin and that those outside Africa migrated out in small groups during the last 60,000 years. His book The Origin of Our Species will be published early next year.

As well as comparing the Neanderthal genome with modern humans, the team also compared it with chimps. They found that genetic changes linked to skin and bone, metabolism, and brain functions, were unique to Homo sapiens.

Previous genetic studies

There have been genetic studies on Neanderthals before, as Prof Stringer explains. ‘The first tiny piece of DNA from a Neanderthal fossil was published in 1997, and since then, with improvements in recovery techniques and computing power, 20 Neanderthals have yielded up increasing amounts of ancient DNA.’

These DNA studies support evidence from the fossil record, showing that Neanderthals split from modern humans around 400,000 years ago. And similarly, studies on DNA from living people support fossil records showing that modern humans share an African origin within the last 200,000 years.

A new look at Neanderthal relations

Prof Stringer concludes, ‘As one of the architects of 'Out of Africa', I have regarded the Neanderthals as representing a separate lineage, and most likely a separate species from Homo sapiens.

‘Although I have never ruled out the possibility of interbreeding, I have considered this to have been small and insignificant in the bigger picture of our evolution – for example, the results of isolated interbreeding events could easily have been lost in the intervening millennia.

‘Now, the Neanderthal genome strongly suggests those genes were not lost, and that many of us outside of Africa have some Neanderthal inheritance.

'Any functional significance of these shared genes remains to be determined, but that will certainly be a focus for the next stages of this fascinating area of research.’